The present invention relates to wetness indicators and, more particularly, to indicator composites incorporating pH indicating agents and to compositions that may be used to make such indicator composites. The indicators may be of a single layer or multiple layer composite, and they may be incorporated in articles and devices wherein it is desirable to sense pH, moisture or wetness.
Chemical compounds that change color with change in pH are well-known in the art. The use of such compounds, or so-called pH indicating agents, to provide pH and wetness indications is also known.
Such wetness indicators are frequently used in connection with disposable diapers. For example, U.S. Pat. No. 3,675,654 includes a translucent backing sheet and an indicating agent applied to an absorbent pad surface adjacent the backing sheet which becomes visible upon moisture contact. U.S. Pat. No. 3,731,685 utilizes capillary action to transmit interior diaper moisture along a strip to an exterior end of the strip having an indicator agent. The pH indicating agent is incorporated in a latex adhesive applied to the backing sheet or adjacent pad surface of a disposable diaper in U.S. Pat. No. 4,231,370. It is also known to incorporate indicating agents in hot melt adhesives used in diapers as disclosed in U.S. Pat. Nos. 4,743,238, 5,035,691, 5,066,711 and 5,089,548. In U.S. Pat. No. 5,354,289, such a hot melt adhesive strip is isolated from the diaper interior by a water impervious baffle that extends beyond the adhesive strip dimensions to cause liquid to flow around the edges of the baffle in order to contact the indicator agent and thereby provide a capacity monitor.
Wetness indicators not using pH indicating agents are also used in disposable diaper constructions to provide visible indicia of diaper wetness. These include water soluble dyes rendered visible by contact with diaper liquid in U.S. Pat. No. 3,675,654. An the opposite approach is used in U.S. Pat. No. 4,022,211 wherein the indicia is visible if dry, but dispersed upon diaper wetting. In other approaches, visibility masks are removed by diaper wetting to allow viewing of the wetness indicia as in U.S. Pat. Nos. 4,192,311 and 4,705,513.
As distinguished from wetness indicators not using pH indicating agents, the present invention contemplates the use of a pH indicating agent for pH or wetness indication of an environment. Herein, an environment comprises a moisture containing fluid. The fluid may be present in liquid and/or in condensable vapor form.